One of the greatest Multiplayer experiences I have ever had. The singleplayer isn't that bad either! I've just been too hooked with M&B MP that I have given M&B SP zero time. I hear nothing but great things from my singleplaying friends though. If you buy this game, I recommend getting the Napoleonic Wars expansion. It's multiplayer only, but that is where I have had the most fun. There are several different game modes. The first is called Siege. In where a defending team must protect their castle from Enemy advancement until the timer has run out, however, keep your head well hidden from them Snipers. As defending team lives are limited to just five. Or less, depending on the time you joined the map. The attackers however, they have unlimited lives but in order to get to you, they must breach a hole in your wall with cannons and then storm the breach; which normally results in your bayonet stuck in their chests as you sing Rule Britannia; or mention the Kaiser if you're playing as Prussia/Austria.
The next gamemode in M&B MP is Battle. In Battle, both teams have just one life. And there is no respawning until the round is complete, so if you charge ahead early on and get mowed down by 6 Cavalry who have joined together and created a small posse, then you're going to be waiting 5-6 minutes for the round to end probably. That can be frustrating so I recommend teaming up with your teammates, rather than go lone wolf assasin style. The game also features TDM and DM gamemodes, I don't need to explain these. As they feature heavily in pretty much every game with a gun or sword and has multiplayer.
Overall, I recommend M&B to anybody if you're a fan of the era it's set in, and are war crazy. Or if you like the RPG and open world elements of the singleplayer. The game also has a VERY strong modding community. And you should try out some of the awesome mods. This was a fantastic experience.